Archived posting to the Leica Users Group, 2015/07/14

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Subject: [Leica] Yet another surprising fact about the M (240)
From: kanner at acm.org (Herbert Kanner)
Date: Tue, 14 Jul 2015 18:55:29 -0700

I was surprised to see in the manual that there was lossless compression of 
the DNG. So I thought I?d try it out by taking two shots, one compressed and 
one uncompressed. When I looked at my DNG file, I was astounded to find a 
DNG of over 40 MB and a compressed one of about half that size. (I deleted 
the negatives before thinking of writing this, so I can?t give you exact 
numbers.

Well, I was at first astounded that lossless compression could be that 
effective. Then I thought about the details of an image. Except where there 
is really fine structure in the image, there will be areas where the data 
does not change. A simple number triple, one giving a value for, say the red 
pixel, the second giving a starting location in the file, and the the third 
the number of consecutively stored pixels having the same value, could 
easily result in a factor of two compression for lots of pictures. And what 
I just described is a very unsophisticated compression method. If anyone 
knows more about how this might have been done, I?d be very interested.

kanner at acm.org
650-326-8204

Question authority and the authorities will question you.






Replies: Reply from richard at richardmanphoto.com (Richard Man) ([Leica] Yet another surprising fact about the M (240))